CODEWITHSUNDEEP
c#c#-6.0
Calle
Calle

Reputation: 1800

How are null values in C# string interpolation handled?

In C# 6.0, string interpolations are added.

string myString = $"Value is {someValue}";

How are null values handled in the above example? (if someValue is null)

EDIT: Just to clarify, I have tested and am aware that it didn't fail, the question was opened to identify whether there are any cases to be aware of, where I'd have to check for nulls before using string interpolation.

Upvotes: 99

Views: 31637

Answers (3)

Vojta Baránek
Vojta Baránek

Reputation: 61

It seems that the behavior depends on which underlying formatting methods are called, and the implementation of these can change over time. If you get a null formated into the string such as "(null)", it is not sure this will stay the same over several years. In some newer version of .NET it can start throwing an exception.

So I think the most safe approach is to make some condition to avoid using the null. Write a simple ternary operation like:

int? someValue = 5;
var valueStr = (someValue is not null) ? someValue.ToString() : string.Empty;
var myString = $"Value is {valueStr}";

It is an extra line of code, but at least the behavior is controlled.

Upvotes: 2

juharr
juharr

Reputation: 32296

That's just the same as string.Format("Value is {0}", someValue) which will check for a null reference and replace it with an empty string. It will however throw an exception if you actually pass null like this string.Format("Value is {0}", null). However in the case of $"Value is {null}" that null is set to an argument first and will not throw.

Upvotes: 71

Soner Gönül
Soner Gönül

Reputation: 98810

From TryRoslyn, it's decompiled as;

string arg = null;
string.Format("Value is {0}", arg);

and String.Format will use empty string for null values. In The Format method in brief section;

If the value of the argument is null, the format item is replaced with String.Empty.

Upvotes: 32

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